1. Field of the Invention
The present invention relates generally to the field of glass lined chemical reactor vessels and more specifically to valves for regulating gravity induced withdrawal of fluids from within such glass lined chemical reactor vessels.
2. Background of the Prior Art
Many of the glass lined chemical reactor vessels currently being used by the chemical processing industries are designed such that the contents thereof can be withdrawn or emptied from such vessels through valving mechanisms located in the bottoms or lowermost areas of such vessels. Reference to the bottoms or lowermost areas indicates that the designation is applied to such vessels when they are set up in their operating positions. These valving mechanisms, likewise, are often glass coated or "lined" on those areas which are exposed to the materials being processed within such vessels. Because both the interior of the vessel and the valving mechanism are glass coated, thus having brittle surfaces and being susceptible to cracking, the surfaces of such vessels must be smooth and designed with gentle transitions for angles and other directional changes of design lines; there can be no sharp corners (corners typically must be smoothly radiused) and no localized stresses which would tend to distort the smooth surfaces of the glass coating and, thus, tend to break, chip or otherwise separate the glass in relation to its bond to the substrate metal. Mating surfaces are generally designed to spread stress and generally include a flat surface-to-flat surface contact, such as, for example, where mating flanges are employed. Such mating surfaces are, also, usually gasketed both to seal the joint and to, essentially, provide a shock absorber for the glassed surfaces.
There are a variety of different arrangements of such valving mechanisms, many of which use flange concepts, face-to-face, with gaskets interposed therebetween. The valving mechanisms are removably mounted to the vessel bodies so that those valving mechanisms can be removed for cleaning, rebuilding, repairs, etc. An example of such a valving mechanism is shown in U.S. Pat. No. 4,473,171. Other generally conceptually similar valves are well known to those with skill in the art.
There are at least two specific industries, within the general chemical processing industry, which find the current state of the art for glass lined chemical reactor vessel valving mechanisms to be less than acceptable. They are the pharmaceutical industry and the food industry. The reason for this is that all of the presently known valving mechanisms for glass lined chemical reactor vessels tend to provide "pockets", "dams" or other aspects of their designs which tend to accumulate and hold contaminants and which are relatively difficult to maintain in a continuously clean, uncontaminated state. For example, a review of FIG. 3 of U.S. Pat. No. 4,473,171 shows a "pocket" formed between element 26 and element 72 above element 76. This pocket is, of course, a trap for contaminants which might, for example, take the form of spoiled food. To clean such a "pocket", the chemical reactor vessel must be emptied and taken out of service, then the valving mechanism must be loosened from the bottom, and finally, a person must climb into the vessel and retrieve the valve body as would be the case in regard to all the valving mechanism shown in U.S. Pat. No. 4,473,171. In other designs, the valving mechanism can be detached from the exterior of the reactor vessel, but the vessel must still be emptied and taken out of service.
What is necessary and desirable is a glass coated valving mechanism for use with glass lined chemical reactor vessels wherein there are relatively no significant "pockets", "dams" or other aspects of design which trap or accumulate contaminants. The use of such a valving mechanism could increase the time cycles between empty, shut down and removal for cleaning and thus increase the efficiency and enhance the economy of operating the chemical reactor vessel.